The present invention relates to a plant monitoring and control system for operation and control of an industrial plant such as a power plant, a chemical plant or the like, and is particularly concerned with a plant monitoring and control system provided with backup means against failure of incorporated controllers.
A bigger plant, such as a power plant, usually has plural control systems divided according to control functions. The plural control systems compose a function-divided control system to disperse risks of a process system shutdown caused by the control system failure.
The function-divided control system has used extensively of late a digital control system according to a progress in semiconductor technique and communication technique. The digital control system is, for example, provided with a remote process input-output unit, a digital process controller, and an operator console at every control system. The operator console is provided with a digital console controller, input units such as key boards, and display units such as CRT's (cathode-ray tube). In addition, all of the remote process input-output units, the process controllers, and the console controllers throughout control systems are connected by a transmission line. The digital-type controllers including the remote process input-output units are designed to be able to perform broadcast communication through the transmission line using a time sharing technique.
That is, plant process variables (e.g. temperature, flow-rate, valve status and so on) are detected by detectors, and detection signals corresponding to the process variables are transmitted into the transmission line for the other controllers by the remote process input-output unit. A process controller takes in, at every assigned time, detection signals and command signals of an operator which are transmitted through the line, and calculates control signals according to a given arithmetic operation procedure. The calculated control signals are then transmitted into the transmission line for the other controllers at every assigned time by the process controller. A remote process input-output unit takes in the control signals at every assigned time and outputs the control signals to process devices to control the process system.
On the other hand, a console controller takes in, at every assigned time, signals corresponding to process status and the operator's command signals, and calculates display signals in accordance with a given procedure. The calculated display signals are visualized on the screen of the display units for the operator to monitor the plant process state. The console controller also acts as an interface unit between the input units and the transmission line.
Moreover, in utilizing the above digital control system, a multiplex construction as a redundant system is essential for enhancing a reliability of monitoring and control of the process which is important for the plant operation. To accomplish the multiplex construction, the plural process controllers, the functions of which are the same for mutual backups, are provided for each control system, and also the plural console controllers of an operator console, the functions of which are the same for mutual backups, are provided for each control system.
However, in the above-described plant monitoring and control system, redundant systems installed for securing a high reliability become complicated in construction and increase system size.